For example, Patent Literature 1 discloses a vehicle frame structure including a pair of main side rails which extends in a vehicle front-rear direction and faces each other and an extension side rail which is connected to a front portion of the main side rail in the vehicle front-rear direction and extends in the vehicle front-rear direction. In the vehicle frame structure, the main side rail is formed to have a substantially C-shaped cross-section and the extension side rail is formed to have a substantially Z-shaped cross-section. At a connection position, both side rails overlap so that the extension side rail is located at the outside of the main side rail.